A digital camera (or an electronic camera) having the function of tracking a moving subject has been known. The digital camera can track the subject and maintain the focus although the subject pursued by a user is moving.
As a related art, a moving region tracking device which stably detects and track a moving region having a plurality of color component regions including achromatic colors. The moving region tracking device includes a moving region detection unit, a color feature extraction unit, a color region reconfiguration unit, a color feature and position information entry unit, a color feature matching moving object detection unit, and a camera control unit. The moving region detection unit detects a plurality of moving regions from a plurality of frames which are captured in different timing in inter-frame difference processing. The color feature extraction unit divides each moving region into small regions, and extracts the color features of the small regions where an area of the moving object is larger than a specified area. The color region reconfiguration unit reconfigures the detected moving region as a moving region formed by a plurality of color regions according to the extracted color features. The color feature and position information entry unit enters the color feature and the position of the reconfigured moving region. The color feature matching moving object detection unit detects a new moving region according to the entered color feature and position, and outputs the moving region to the color feature and position information entry unit. The camera control unit determines the control condition of a CCD camera based on the new moving region, and performs tracking process. (For example, Japanese Laid-open Patent Publication No. 11-136664).
As another related art, a method for separating each granular object in various shapes from an image in which a plurality of granular objects contact one another is known. In this method, an image of a medicine captured by an imaging device is binarized. The digital image analysis and determination unit distributes and arranges a plurality of reference points to the area near the contour of the medicine area in the binary image, and then generates connection lines by connecting a reference point to another reference point so that a combination of reference points as a group includes no connection line passing outside the medicine area. Thus, all reference points correspond to any group, and a reference point group respectively corresponds to an individual area as an image area of the medicine in the binary image, thereby checking a test item of the medicine. (For example, Japanese Laid-open Patent Publication No. 2004-234132)
Another related art, a shape determining method for correctly determining a germ is known. This method extracts the region of a test object to be determined for its shape from a captured image, calculates the contour of the test object, calculates the center line of the test object, detects the bent portion of the test object based on the center line, calculates the thickness of the test object of the region excluding the bent portion according to the contour calculated in the contour calculating step, calculates the average of the thickness, calculates the variance of the thickness, calculates the length of the test object based on the length of the center line, and determines the shape of the test object based on the average of the thickness, the variance of the thickness, and the length of the test object. (For example, Japanese Laid-open Patent Publication No. 2008-298706)
In the conventional technique, when there are a plurality of regions having the identical or similar color component in the image data, there may be a case in which each region is not appropriately recognized. For example, assume that a first subject to be tracked and a second subject not to be tracked are captured by a digital camera. Also assume that the first and second subjects are similar in color to each other. Then, the object tracking device tracks the first subject using the color component of the image data obtained by the digital camera. In this case, when the color regions corresponding to the first and second subjects overlap each other in the image data, one color region is detected and then it is difficult to identify the first subject from the second subject. In addition, when the color regions corresponding to the first and second subjects once overlap each other in the image data and are then separated, the object tracking device may erroneously track the second subject.
In the above-mentioned related techniques, it is assumed that the shape or the size of a subject is known. That is, when the shape of the subject is unknown, there is a case in which a target object is not correctly tracked.